This invention pertains to the art of centrifugal clutches, and particularly to the art of clutches useful in transport refrigeration units.
A conventional method for providing either internal combustion engine drive or electric motor drive for a refrigerant compressor, such as is used with a transport refrigeration unit, includes an internal combustion engine such as a diesel driving the compressor through a centrifugal clutch and belt and an electric motor which can also drive the compressor through a belt when the engine is not running and the clutch is disengaged.
One commonly used centrifugal clutch arrangement for smaller transport refrigeration units, such as for refrigerated straight trucks, has a pair of clutch shoes mounted to the driving rotor or hub through pivot posts and resilient bushings with a spring system to retract the shoes when the hub is not rotating. Such a centrifugal clutch is used in a refrigeration unit where the refrigerant compressor can be belt driven either by an internal cumbustion engine through the clutch or, alternatively, by an electric motor -- the clutch being disengaged of course when the engine is stopped. These conventional clutches have failed in sufficient quantities to create a significant warranty problem for the refrigeration unit manufacturer.
It is my view that many of the failures stem from severe torque peaks generated by the internal combustion engine under certain conditions imposing structural damage to the clutch parts, such as breaking the pivot posts at their connection to the hub or bending them, or damaging the resilient bushings in the bores of the shoes. Such torque peaks are more severe with diesel engines than with gasoline engines and are also related to the number of engine cylinders--the fewer the cylinders the greater the problem. As an example in numerical terms of the severity of the torque peaks, the conventional clutch used by the assignee of this application may be rated at, say, 50 foot pounds (82J) torque, while under some conditions it may be subjected to torque peaks up to 500 foot pounds (680J).
The aim of this invention is to provide a different clutch arrangement in which the torque peaks are so absorbed that clutch failures are reduced, as well as to provide a relatively simple clutch construction in which shoe pivot posts are eliminated along with elastomeric bushings associated with the shoes and posts.